I have been using mesh floors for some time & I'm still using apiguard till I run out.
It's thymol based gel which doesn't kill the mites but irritates them sufficiently to get them to drop off, so no resistance build up as with the old bayvorol/apistan strips (Flumethrin) .
I think beevital & a lot of the other 'natural' remedies are similar.
When I run out of apiguard I'm going to use (again Gareth) LINK
Having bees that aren't over prolific helps.
Some bees build up so fast & in such high numbers that if you don't treat at the right time they can quickly become infested.
Checking your mite count on a weekly basis is good.
Gives you an indicator of when treatment is necessary.
I've got to be honest & say I don't check my mite drop like I should, but the bees I have are hardy survivors that came from a neglected WBC hive at a friends place & had no varroa treatment (or anything done to them at all) for eight or ten years before I got them so I figure if they survived that, they can survive my lack of diligence.